In U.S. Pat. No. 4,744,615, an arrangement for reducing coherence is disclosed in an embodiment having a light tunnel. The light must be fed into the light tunnel divergently and leaves the tunnel with intense divergence.
A paper by J. Wangler et al entitled "Design principles for an illumination system using an excimer laser as a light source", Proceeding ELO II, Volume 1138, page 129, Paris 1989, discloses various alternatives including a moved diffusion screen, lenticular array and non-imaging concentrator which are similar to embodiments disclosed in the above-mentioned United States Patent. Furthermore, this paper discloses the use and the requirements for UV-lithography.
In U.S. Pat. No. 4,686,542, the use of a plane-parallel plate having one side which is fully reflecting and another which is partially reflecting is described for splitting a laser beam into several separate parallel beams for a raster output scanner. The partially reflecting surface of the plane-parallel plate is partially reflecting in such a manner that a stepwise reduction in the degree of reflection is provided.